Joining tables that compute values between dates

Question

so I have the two following tables

Table A

Date        num
01-16-15    10
02-20-15    12
03-20-15    13

Table B

Date           


        

Answer 1

This works on MariaDb (MySql) and it's pretty basic so hopefully it works on impala too.

SELECT b.date, b.value * a.num
FROM tableB b, tableA a
WHERE b.date >= a.date
  AND (b.date < (SELECT MIN(c.date) FROM tableA c WHERE c.date > a.date)
       OR NOT EXISTS(SELECT c.date FROM tableA c WHERE c.date > a.date))

The last NOT EXISTS... was needed to include dates after the last date in table A

Update In the revised version of the question the date in B is never larger (after) the last date in A so then the query can be written as

SELECT b.date, b.value * a.num
FROM tableB b, tableA a
WHERE b.date >= a.date
  AND b.date <= (SELECT MIN(c.date) FROM tableA c WHERE c.date > a.date)